Unfortunately, Canvas won't show embedded images (residing in Canvas) in the email of announcements. I searched at the Canvas Community forums and folks have been complaining about this problem for literally years, and nothing has been done about it. This is clearly an essential feature. Their suggestion is to tell students to click on View Announcement (link at the bottom of email) and view it in Canvas.
I don't know if they plan to eventually address this, but it's not supported at this time.
BTW - to get notifications from the forums on replies to your posts, you will need to be logged on. If you don't have an account, click on Register at the top and create one, and post while you are logged on (you can have your browser to store your login).